ios - CoreData: Fetching entities with special condition -

in database, have entity called "address", there 140k rows of addresses. each address has attributes "lat" , "lng", indicating latitude , longitude of address.

provided have acquired user location location service, how traversing addresses , find address nearest user location?

i have code construct haversine distance if can latitude , longitude of address, problem don't know how in predicate.

my current code getting nearest addreses array:

// user location acquired location service cllocationcoordinate2d currentlocationcoordinate = location.coordinate; float dist = flt_max; int nearestaddressindex = -1; for(int = 0; < [addresses count]; ++i) {     nsdictionary *address = addresses[i];     haversine *haverobject = [[haversine alloc] initwithlat1:currentlocationcoordinate.latitude                                                         lon1:currentlocationcoordinate.longitude                                                         lat2:[address[@"lat"] floatvalue]                                                         lon2:[address[@"lng"] floatvalue]];     if ([haverobject tometers] < dist ) {         dist = [haverobject tometers];         nearestaddressindex = i;     } } 

is there way construct predicate? or must fetching addresses in array , traversing array?

i bit reluctant latter, worry might cause app terminate due memory pressure.

also similar question occur somewhere else in app:

in second case, need address falls within radius around user location. below code array:

cllocationcoordinate2d currentlocationcoordinate = location.coordinate; cgfloat threshold = 500.0f; nsmutablearray *nearbystation = [nsmutablearray array];  (nsdictionary *station in [datahelper sharedinstance].stations) {     cgfloat lat = [station[@"lat"] floatvalue];     cgfloat lng = [station[@"lng"] floatvalue];      haversine *haverobject = [[haversine alloc] initwithlat1:currentlocationcoordinate.latitude                                                         lon1:currentlocationcoordinate.longitude                                                         lat2:lat                                                         lon2:lng];     if ([haverobject tometers] <= threshold)     {         [nearbystation addobject:station];     } } 

i have above code datas stored in array. how same thing "address" stored in core data?

it's better if traverse 1 value of entity. try adapting this:

nsentitydescription *description = [nsentitydescription entityforname:@"address"                                                inmanagedobjectcontext:[yourcontext managedobjectcontext]]; nsfetchrequest *request = [[nsfetchrequest alloc] init]; [request setentity:description]; nspredicate *predicate = [nspredicate predicatewithformat:@"examplelatitute < dist"]; [request setpredicate:predicate]; nserror *error = nil; nsarray *array = [[yourcontext managedobjectcontext] executefetchrequest:request                                                                    error:&error];